KR20150090010A - Method and apparatus for image encoding, and method and apparatus for image decoding - Google Patents

Abstract

Disclosed are a method and an apparatus for image encoding, and a method and an apparatus for image decoding to partition a current picture into blocks in different sizes and to variously set the number of intra-prediction modes applied in accordance with the size of the partitioned blocks.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method and apparatus,

The present invention relates to encoding and decoding of an image, and more particularly, to a method and apparatus for encoding and decoding an image that performs intra prediction by selecting an intra prediction mode in various directions.

In an image compression method such as MPEG-1, MPEG-2, MPEG-4, and H.264 / MPEG-4 Advanced Video Coding (AVC), one picture is divided into macroblocks to encode an image. Then, each macroblock is encoded in all coding modes available for inter prediction and intra prediction, and then an encoding mode is selected according to the bit rate required for encoding the macroblock and the degree of distortion between the original macroblock and the decoded macroblock. And the macro block is encoded.

Background of the Invention [0002] As the development and dissemination of hardware capable of playing back and storing high-resolution or high-definition video content increases the need for video codecs to effectively encode or decode high-definition or high-definition video content. According to the existing video codec, video is encoded according to a limited prediction mode based on a macroblock of a predetermined size.

The present invention relates to an image encoding method using intra-prediction methods having various directions based on hierarchical encoding units of various sizes. A decoding method and apparatus are provided.

The image encoding apparatus according to an embodiment of the present invention includes: a division unit for dividing the image into a maximum-size maximum encoding unit and dividing the maximum encoding unit into hierarchical encoding units; An intra prediction unit for determining an intra prediction mode of a prediction unit for performing prediction of a current coding unit to be coded among the coding units and performing intra prediction for the prediction unit according to the determined intra prediction mode, The intra-prediction mode indicates a specific direction among a plurality of directions, and the specific direction is dx (dx is an integer) representing the number of pixels in the horizontal direction and dy (dy is an integer) representing the number of pixels in the vertical direction. Wherein the intra prediction unit predicts, based on the position of the current pixel of the prediction unit and the specific direction indicated by the intra prediction mode, at least one of the left and right of the prediction unit Acquires a peripheral pixel of the image, And obtains a predicted value of the current pixel.

The image decoding apparatus according to an embodiment of the present invention extracts information on a maximum size of an encoding unit from a bitstream and division information indicating whether a current encoding unit of the current depth is divided into low resolution encoding units, Determining a prediction unit for performing a prediction of an encoding unit of a current depth to be decoded among the encoding units, determining a prediction unit for performing a prediction of a current encoding unit from among the encoding units, An entropy decoding unit for extracting intra prediction mode information of a unit; And an intra predictor for performing intra prediction on the prediction unit according to the extracted intra prediction mode, wherein the intra prediction mode indicates a specific direction among a plurality of directions, and the specific direction is a number of pixels in the horizontal direction And dy (dy is an integer) pixels indicating the number of pixels in the vertical direction, and the intraprediction unit detects the position of the current pixel of the prediction unit and the position of the current pixel of the prediction unit, Acquiring at least one neighboring pixel positioned at one of left and upper sides of the prediction unit according to the specific direction indicated by the intra prediction mode and acquiring a predicted value of the current pixel using the obtained neighboring pixels .

According to the present invention, intraprediction encoding is performed in various directions for encoding units of various sizes, thereby improving the compression efficiency of an image.

1 is a block diagram of an image encoding apparatus according to an embodiment of the present invention.
2 is a block diagram of an image decoding apparatus according to an embodiment of the present invention.
FIG. 3 illustrates a hierarchical encoding unit according to an embodiment of the present invention.
4 is a block diagram of an image encoding unit based on an encoding unit according to an embodiment of the present invention.
5 is a block diagram of an image decoding unit based on an encoding unit according to an embodiment of the present invention.
FIG. 6 illustrates a depth-based coding unit and a prediction unit according to an embodiment of the present invention.
FIG. 7 shows a relationship between an encoding unit and a conversion unit according to an embodiment of the present invention.
FIG. 8 illustrates depth-specific encoding information, in accordance with an embodiment of the present invention.
FIG. 9 shows a depth encoding unit according to an embodiment of the present invention.
FIGS. 10A to 10C show a relationship between an encoding unit, a prediction unit, and a frequency conversion unit according to an embodiment of the present invention.
FIG. 11 shows encoding information for each encoding unit according to an embodiment of the present invention.
FIG. 12 shows the number of intra prediction modes according to the size of an encoding unit according to an embodiment of the present invention.
13A to 13C are views for explaining an example of an intra prediction mode applied to a coding unit of a predetermined size according to an embodiment of the present invention.
14 is a view for explaining another example of an intra prediction mode applied to a coding unit of a predetermined size according to an embodiment of the present invention.
15 is a reference diagram for explaining intra prediction modes having various directions according to an embodiment of the present invention.
16 is a reference diagram for explaining a bilinear mode according to an embodiment of the present invention.
17 is a diagram for explaining a process of generating a prediction value of an intra prediction mode of a current encoding unit according to an embodiment of the present invention.
18 is a reference diagram for explaining a process of mapping an intra prediction mode between coding units having different sizes according to an embodiment of the present invention.
19 is a reference diagram for explaining a process of mapping intra-prediction modes of a surrounding encoding unit to one of representative intra-prediction modes according to an embodiment of the present invention.
20 is a block diagram illustrating an apparatus for intra prediction of an image according to an embodiment of the present invention.
FIG. 21 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.
22 is a flowchart illustrating a video decoding method according to an embodiment of the present invention.

According to the maximum size of the coding unit, the image data of the current picture is divided into a maximum coding unit, and each maximum coding unit may include coding units divided by depth. Since the maximum encoding unit according to an embodiment of the present invention is divided by depth, image data of a spatial domain included in the maximum encoding unit can be hierarchically classified according to depth.

The maximum depth for limiting the total number of times the height and width of the maximum encoding unit can be hierarchically divided and the maximum size of the encoding unit may be preset. The maximum encoding unit and the maximum depth may be set in units of pictures or slices. That is, each picture or slice may have a different maximum coding unit and maximum depth, and the minimum coding unit size included in the maximum image coding unit may be variably set according to the maximum depth. By setting the maximum coding unit and the maximum depth for each picture or slice in this manner, it is possible to improve the compression ratio by coding the image of the flat area using a larger maximum coding unit, and the image with a large complexity can be encoded The compression efficiency of the image can be improved by using the unit.

The encoding depth determination unit 120 encodes at least one divided area in which the area of the maximum encoding unit is divided for each depth, and determines the depth at which the final encoding result is output for each of at least one of the divided areas. That is, the coding depth determination unit 120 selects the depth at which the smallest coding error occurs, and determines the coding depth as the coding depth by coding the image data in units of coding per depth for each maximum coding unit. The coding depth may be determined based on a Rate-Distortion Cost calculation. The determined coding depth and the image data of each coding unit are output to the output unit 130.

The image data in the maximum encoding unit is encoded based on the depth encoding unit according to at least one depth below the maximum depth, and the encoding results based on the respective depth encoding units are compared. As a result of the comparison of the encoding error of the depth-dependent encoding unit, the depth with the smallest encoding error can be selected. At least one coding depth may be determined for each maximum coding unit.

As the depth of the maximum encoding unit increases, the encoding unit is hierarchically divided and reduced, and the number of encoding units increases. In addition, even if encoding units of the same depth included in one maximum encoding unit, the encoding error of each data is measured and it is determined whether or not the encoding unit is divided into lower depths. Therefore, even if the data included in one maximum coding unit has a different coding error according to the position, the coding depth can be determined depending on the position. In other words, the maximum encoding unit may be divided into sub-encoding units of different sizes according to different depths. One or more coding depths may be set for one maximum coding unit and data of the maximum coding unit may be divided according to the coding units of one or more coding depths.

Further, the sub-encoding units of different sizes included in the maximum encoding unit can be predicted or frequency-converted based on the processing units of different sizes. In other words, the image encoding apparatus 100 can perform a plurality of processing steps for image encoding based on various sizes and processing units of various types. In order to encode video data, processing steps such as prediction, frequency conversion, and entropy encoding are performed. Processing units of the same size may be used in all stages, and processing units of different sizes may be used in each step.

For example, in order to predict a coding unit, the image coding apparatus 100 may select a coding unit and a different processing unit. For example, when the size of the encoding unit is 2Nx2N (where N is a positive integer), the processing unit for prediction may be 2Nx2N, 2NxN, Nx2N, NxN, and the like. In other words, predictive coding may be performed based on a processing unit of a type in which at least one of the height or the width of an encoding unit is halved. Hereinafter, a data unit serving as a basis of predictive encoding is referred to as a 'prediction unit'.

The prediction mode may be at least one of an intra mode, an inter mode, and a skip mode, and the specific prediction mode may be performed only for a prediction unit of a specific size or type. For example, the intra mode can be performed only for a 2Nx2N, NxN sized prediction unit, which is a square. In addition, the skip mode can be performed only for a prediction unit of 2Nx2N size. If there are a plurality of prediction units in an encoding unit, a prediction mode having the smallest coding error can be selected by performing prediction for each prediction unit.

Also, the image encoding apparatus 100 can frequency-convert image data based on a processing unit having a different size from the encoding unit. The frequency conversion may be performed based on a data unit having a size smaller than or equal to the encoding unit for frequency conversion of the encoding unit. Hereinafter, a processing unit serving as a basis of frequency conversion is referred to as a 'conversion unit'.

The coding depth determiner 120 measures the coding error of each depth coding unit using a Lagrangian Multiplier based Rate-Distortion Optimization technique and calculates the maximum coding unit having the optimal coding error Can be determined. In other words, the coding depth determiner 120 can determine which type of the maximum coding unit is divided into a plurality of sub-coding units, wherein the plurality of sub-coding units have different sizes depending on the depth.

The output unit 130 outputs, in the form of a bit stream, video data of the maximum encoding unit encoded based on at least one encoding depth determined by the encoding depth determination unit 120 and information on the depth encoding mode.

The information on the depth-dependent coding mode may include coding depth information, partition type information of a prediction unit of a coding unit of coding depth, prediction mode information per prediction unit, size information of a conversion unit, and the like.

The coding depth information can be defined using depth division information indicating whether or not coding is performed at the lower depth coding unit without coding at the current depth. If the current depth of the current encoding unit is the encoding depth, the current encoding unit is encoded in the current depth encoding unit, so that the division information of the current depth can be defined so as not to be further divided into lower depths. On the other hand, if the current depth of the current encoding unit is not the encoding depth, the encoding using the lower depth encoding unit should be tried. Therefore, the division information of the current depth may be defined to be divided into the lower depth encoding units.

If the current depth is not the encoding depth, encoding is performed on the encoding unit divided into lower-depth encoding units. Since there are one or more lower-level coding units in the current-depth coding unit, the coding is repeatedly performed for each lower-level coding unit so that recursive coding can be performed for each coding unit of the same depth.

At least one coding depth is determined in one maximum coding unit and at least one coding mode information is determined for each coding depth so that information on at least one coding mode can be determined for one maximum coding unit. In addition, since the data of the maximum encoding unit is hierarchically divided according to the depth and the depth of encoding may be different for each position, information on the encoding depth and the encoding mode can be set for the data.

Accordingly, the output unit 130 according to the embodiment can set the corresponding encoding information for each minimum encoding unit included in the maximum encoding unit. That is, the coding unit of the coding depth includes at least one minimum coding unit that holds the same coding information. By using this, if the neighboring minimum encoding units have the same depth encoding information, it can be the minimum encoding unit included in the same maximum encoding unit.

For example, the encoding information output through the output unit 130 may be classified into encoding information per depth unit and encoding information per prediction unit. The under-coding-by-depth coding unit information may include prediction mode information and partition size information. The encoding information to be transmitted for each prediction unit includes information about the estimation direction of the inter mode, information about the reference picture index of the inter mode, information on the motion vector, information on the chroma component of the intra mode, information on the interpolation mode of the intra mode And the like. Information on the maximum size of a coding unit defined for each picture, slice or GOP, and information on the maximum depth can be inserted into the header of the bitstream.

According to the simplest embodiment of the image coding apparatus 100, the depth-dependent coding unit is a coding unit having a height divided by the height and width of the coding unit of one layer higher depth. That is, if the size of the encoding unit of the current depth (k) is 2Nx2N, the size of the encoding unit of the lower depth (k + 1) is NxN. Therefore, the current encoding unit of 2Nx2N size can include a maximum of 4 sub-depth encoding units of NxN size.

Therefore, the image decoding apparatus 100 according to an exemplary embodiment can determine an optimum shape division type for each maximum encoding unit based on the size and the maximum depth of the maximum encoding unit determined in consideration of the characteristics of the current picture. In addition, since each encoding unit can be encoded by various prediction modes, frequency conversion methods, and the like, an optimal encoding mode can be determined in consideration of image characteristics of encoding units of various image sizes.

If an image having a very high image resolution or a very large data amount is encoded in units of a conventional 16x16 macroblock, the number of macroblocks per picture becomes excessively large. This increases the amount of compression information generated for each macroblock, so that the burden of transmission of compressed information increases and the data compression efficiency tends to decrease. Therefore, the image encoding apparatus according to the embodiment of the present invention can increase the maximum size of the encoding unit in consideration of the image size, and adjust the encoding unit in consideration of the image characteristic, so that the image compression efficiency can be increased .

2 is a block diagram of an image decoding apparatus according to an embodiment of the present invention.

2, an apparatus 200 for decoding an image according to an exemplary embodiment of the present invention includes a receiving unit 210, an image data and coding information extracting unit 220, and an image data decoding unit 230.

The receiving unit 210 receives and parses a bitstream of the encoded video. The image data and encoding information extracting unit 220 extracts image data for each maximum encoding unit from the parsed bit stream and outputs the extracted image data to the image data decoding unit 230. The image data and encoding unit extraction unit 220 can extract information on the maximum encoding unit of the current picture or slice from the header of the current picture or slice.

Also, the image data and encoding information extracting unit 220 extracts information on the encoding depth and the encoding mode for each maximum encoding unit from the parsed bitstream. The information on the extracted coding depth and coding mode is output to the image data decoding unit 230.

Information on the coding depth and the coding mode per coding unit can be set for one or more coding depth information, and the information on the coding mode for each coding depth includes information on partition type information, prediction mode information, Size information of the conversion unit, and the like. In addition, as the encoding depth information, depth-based segmentation information may be extracted.

The information on the division type of the maximum encoding unit may include information on sub-encoding units of different sizes according to the depth included in the maximum encoding unit, the information on the encoding mode may include information on a prediction unit for each sub- Information on the prediction mode, information on the conversion unit, and the like.

The image data decoding unit 230 decodes the image data of each maximum encoding unit based on the information on the encoding depth and the encoding mode for each maximum encoding unit to reconstruct the current picture. The image data decoding unit 230 can decode the sub-encoding unit included in the encoding unit of the maximum encoding depth, based on the information on the division type of the maximum encoding unit. The decoding process may include a prediction process including intra prediction and motion compensation and an inverse frequency conversion process.

The image data decoding unit 230 performs intra prediction or motion prediction in each prediction unit and prediction mode for each coding unit on the basis of the division type information and the prediction mode information of the prediction unit of the coding unit for each coding depth, Compensation can be performed. In addition, the image data decoding unit 230 may perform inverse conversion on each conversion unit for each encoding unit, based on the size information of the conversion unit of the encoding unit by encoding depth, for inverse conversion for each maximum encoding unit.

The image data decoding unit 230 can determine the coding depth of the current maximum encoding unit using the division information by depth. If the partition information indicates that the current depth is to be decoded, the current depth is the depth of the encoding. Therefore, the image data decoding unit 230 can decode the current depth encoding unit for the image data of the current maximum encoding unit using the partition type, the prediction mode, and the conversion unit size information of the prediction unit. That is, it is possible to observe the encoding information set for the minimum encoding unit and to decode the minimum encoding units that hold the encoding information including the same division information, into one data unit.

The image decoding apparatus 200 according to an exemplary embodiment recursively performs encoding for each maximum encoding unit in the encoding process to obtain information on the encoding unit that has generated the minimum encoding error and can use it for decoding the current picture have. That is, it is possible to decode video data in the optimal encoding unit for each maximum encoding unit. Accordingly, even if an image with a high resolution or an excessively large amount of data is used, the information on the optimal encoding mode transmitted from the encoding end is used, and the image data is efficiently encoded according to the encoding unit size and encoding mode, Can be decoded and restored.

FIG. 3 illustrates a hierarchical encoding unit according to an embodiment of the present invention.

Referring to FIG. 3, the hierarchical coding unit according to the present invention may include 32x32, 16x16, 8x8, and 4x4 from a coding unit having a width x height of 64x64. In addition to the square-shaped encoding units, there may be encoding units whose width x height is 64x32, 32x64, 32x16, 16x32, 16x8, 8x16, 8x4, 4x8.

3, the resolution is set to 1920 x 1080, the size of the maximum encoding unit is set to 64, and the maximum depth is set to 2 for the video data 310. For the video data 320, the resolution is set to 1920 x 1080, the maximum size of the encoding unit is set to 64, and the maximum depth is set to 4. [ For the video data 330, the resolution is set to 352 x 288, the maximum size of the encoding unit is set to 16, and the maximum depth is set to 2.

It is desirable that the maximum size of the encoding size is relatively large in order to accurately reflect not only the compression ratio but also the image characteristic when the resolution is high or the data amount is large. Therefore, the maximum size of the video data 310 and 320 having the higher resolution than the video data 330 can be selected to be 64. FIG.

The maximum depth indicates the total number of layers in the hierarchical encoding unit. Therefore, since the maximum depth of the video data 310 is 2, the encoding unit 315 of the video data 310 is encoded from a maximum encoding unit having a major axis size of 64, Units. On the other hand, since the maximum depth of the video data 330 is 2, the encoding unit 335 of the video data 330 has a depth of two layers from the encoding units having the major axis size of 16, Units.

Since the maximum depth of the video data 320 is 4, the encoding unit 325 of the video data 320 has a depth of four layers from 32 to 16, 8, and 4 Encoding units. Since the image is encoded based on a smaller sub-encoding unit as the depth is deeper, it is suitable to encode an image including a finer scene.

4 is a block diagram of an image encoding unit based on an encoding unit according to an embodiment of the present invention.

The image encoding unit 400 according to an exemplary embodiment of the present invention performs image data encoding operations to be performed in order to determine the encoding depth in the encoding depth determination unit 120 of the image encoding apparatus 100 of FIG.

4, the intra-prediction unit 410 performs intra-prediction on a prediction unit of an intra mode in the current frame 405, and the motion estimation unit 420 and the motion compensation unit 425 perform intra- Inter prediction and motion compensation are performed using the current frame 405 and the reference frame 495 with respect to the unit.

The residual values are generated based on the prediction unit output from the intra prediction unit 410, the motion estimation unit 420 and the motion compensation unit 425, and the generated residual values are input to the frequency conversion unit 430 and the quantization unit 420. [ (440) and output as quantized transform coefficients.

The quantized transform coefficients are restored to a residual value through the inverse quantization unit 460 and the frequency inverse transform unit 470. The restored residual values are passed through the deblocking unit 480 and the loop filtering unit 490, And output to the reference frame 495. [ The quantized transform coefficient may be output to the bitstream 455 via the entropy encoding unit 450.

In order to perform encoding according to the image encoding method according to an embodiment of the present invention, an intra prediction unit 410, a motion estimation unit 420, a motion compensation unit 425, The inverse quantization unit 460, the inverse quantization unit 470, the deblocking unit 480 and the loop filtering unit 490 of the quantization unit 430, the quantization unit 440, the entropy coding unit 450, the inverse quantization unit 460, , Sub-encoding units according to depth, prediction units, and conversion units. In particular, the intra prediction unit 410, the motion estimation unit 420, and the motion compensation unit 425 determine the prediction unit and the prediction mode in the coding unit in consideration of the maximum size and depth of the coding unit, and the frequency conversion unit 430 ) Can consider the size of the conversion unit considering the maximum size and depth of the encoding unit.

5 is a block diagram of an image decoding unit based on an encoding unit according to an embodiment of the present invention.

Referring to FIG. 5, the bitstream 505 is parsed by the parser 510, and the encoded image data to be decoded and the encoding information necessary for decoding are parsed. The encoded image data is output as inverse-quantized data through the entropy decoding unit 520 and the inverse quantization unit 530, and is restored to the residual values through the frequency inverse transform unit 540. [ The residual values are added to the intraprediction result of the intraprediction unit 550 or the motion compensation result of the motion compensation unit 560, and restored for each encoding unit. The reconstructed coding unit is used for predicting the next coding unit or the next picture through the deblocking unit 570 and the loop filtering unit 580.

A parsing unit 510, an entropy decoding unit 520, an inverse quantization unit 530, an inverse frequency transforming unit (hereinafter referred to as an inverse quantization unit) 530, The intra prediction unit 550, the motion compensation unit 560, the deblocking unit 570 and the loop filtering unit 580 are all based on the maximum encoding unit, the depth-dependent sub-encoding unit, the prediction unit, And can process the image decoding processes. In particular, the intra prediction unit 550 and the motion compensation unit 560 determine a prediction unit and a prediction mode in an encoding unit in consideration of the maximum size and depth of an encoding unit, and the frequency inverse transform unit 540 transforms the maximum size And the depth of the conversion unit can be taken into consideration.

FIG. 6 illustrates a depth-based coding unit and a prediction unit according to an embodiment of the present invention.

The image encoding apparatus 100 and the image decoding apparatus 200 according to an embodiment use a hierarchical encoding unit to consider image characteristics. The maximum height, width, and maximum depth of the encoding unit may be adaptively determined according to the characteristics of the image, or may be variously set according to the demand of the user. The size of each coding unit may be determined according to a maximum size of a predetermined coding unit.

The hierarchical structure 600 of the encoding unit according to an embodiment of the present invention shows a case where the maximum height and width of the encoding unit is 64 and the maximum depth is 4. Since the depth is deeper along the vertical axis of the hierarchical structure 600 of the encoding unit according to the embodiment, the height and width of each depth-dependent encoding unit are divided. In addition, along the horizontal axis of the hierarchical structure 600 of the coding unit, a prediction unit which is a partial data unit which is a prediction base of each coding unit of depth is shown.

The maximum coding unit 610 is the largest coding unit among the hierarchical structures 600 of the coding units and has a depth of 0, and the size of the coding units, i.e., the height and the width, is 64x64. A depth-1 encoding unit 620 having a size of 32x32, a depth-2 encoding unit 620 having a size 16x16, a depth-3 encoding unit 640 having a size 8x8, a depth 4x4 having a size 4x4, There is an encoding unit 650. An encoding unit 650 of depth 4 of size 4x4 is the minimum encoding unit.

Referring also to FIG. 6, partial data units are shown along the horizontal axis for each depth, as a prediction unit of an encoding unit. That is, the prediction unit of the maximum encoding unit 610 having a depth 0 size of 64x64 is a partial data unit 610 of size 64x64, partial data units 612 of size 64x32 included in the encoding unit 610 of size 64x64, Partial data units 614 of size 32x64, and partial data units 616 of size 32x32.

The prediction unit of the 32x32 coding unit 620 having the depth 1 is the partial data unit 620 of the size 32x32 included in the coding unit 620 of the size 32x32, the partial data units 622 of the size 32x16, Partial data units 624 of size 16x16, and partial data units 626 of size 16x16.

The prediction unit of the 16x16 coding unit 630 of depth 2 is a partial data unit 630 of size 16x16, partial data units 632 of size 16x8, a size of 8x16 16x16 included in the coding unit 630 of size 16x16, Partial data units 634 of size 8x8, and partial data units 636 of size 8x8.

The prediction unit of the encoding unit 640 having the depth 3 of 8x8 is a partial data unit 640 of the size 8x8, partial data units 642 of the size 8x4, a size 4x8 of the size 8x8 included in the encoding unit 640 of the size 8x8, Partial data units 644 of size 4x4, and partial data units 646 of size 4x4.

Finally, a coding unit 650 of size 4x4 is the minimum coding unit and the coding unit of the lowest depth, and the prediction unit is a data unit 650 of size 4x4.

In order to determine the depth of encoding of the maximum encoding unit 610, the encoding depth determining unit 120 of the image encoding apparatus according to an exemplary embodiment may perform encoding for each depth unit included in the maximum encoding unit 610 Should be performed.

The number of coding units per depth to include data of the same range and size increases as the depth of the coding unit increases. For example, for data containing one coding unit at depth 1, four coding units at depth 2 are required. Therefore, in order to compare the encoding results of the same data by depth, they should be encoded using a single depth 1 encoding unit and four depth 2 encoding units, respectively.

For each depth-of-field coding, encoding is performed for each prediction unit of the depth-dependent coding unit along the horizontal axis of the hierarchical structure 600 of the coding unit, and a representative coding error, which is the smallest coding error at the corresponding depth, is selected . In addition, depths are deepened along the vertical axis of the hierarchical structure 600 of encoding units, and the minimum encoding errors can be retrieved by comparing the representative encoding errors per depth by performing encoding for each depth. The depth at which the minimum coding error occurs among the maximum coding units 610 can be selected as the coding depth and the partition type of the maximum coding unit 610. [

FIG. 7 shows a relationship between an encoding unit and a conversion unit according to an embodiment of the present invention.

The image encoding apparatus 100 and the image decoding apparatus 200 according to an embodiment of the present invention divide and encode or decode an image with a coding unit smaller than or equal to the maximum encoding unit for each maximum encoding unit. The size of the conversion unit for frequency conversion during encoding can be selected based on data units that are not larger than the respective encoding units. For example, when the current encoding unit 710 is 64x64, the frequency conversion can be performed using the 32x32 conversion unit 720. [ In addition, the data of the encoding unit 710 of 64x64 size is encoded by performing the frequency conversion with the conversion units of 32x32, 16x16, 8x8, and 4x4 size of 64x64 or smaller, respectively, and then the conversion unit having the smallest error with the original Can be selected.

FIG. 8 illustrates depth-specific encoding information, in accordance with an embodiment of the present invention.

The encoding information encoding unit of the image encoding apparatus 100 according to an embodiment of the present invention includes information on the encoding mode, information 800 about the partition type, information on the prediction mode 810 ), And information 820 on the conversion unit size may be encoded and transmitted.

The partition type information 800 indicates a prediction unit for predictive encoding of the current encoding unit and information on the type in which the current encoding unit is divided. For example, the current encoding unit CU_0 of depth 0 and size 2Nx2N includes a prediction unit 802 of size 2Nx2N, a prediction unit 804 of size 2NxN, a prediction unit 806 of size Nx2N, a prediction unit 808 of size NxN ) And can be used as a prediction unit. In this case, information 800 regarding the partition type of the current encoding unit includes a prediction unit 802 of size 2Nx2N, a prediction unit 804 of size 2NxN, a prediction unit 806 of size Nx2N, and a prediction unit 808 of size NxN. Lt; / RTI >

The information 810 on the prediction mode indicates the prediction mode of each prediction unit. The prediction unit indicated by the information 800 relating to the partition type is predicted to be one of the intra mode 812, the inter mode 814 and the skip mode 816 through the prediction mode information 810, for example. Can be set.

In addition, the information 820 on the conversion unit size indicates whether to perform frequency conversion on the basis of which conversion unit the current encoding unit is performed. For example, the conversion unit may be one of a first intra-conversion unit size 822, a second intra-conversion unit size 824, a first inter-conversion unit size 826, have.

The encoding information extracting unit of the video decoding apparatus 200 according to an embodiment of the present invention extracts the information 800 about the partition type, the information 810 about the prediction mode, Information 820 can be extracted and used for decoding.

FIG. 9 shows a depth encoding unit according to an embodiment of the present invention.

Partition information may be used to indicate changes in depth. The division information indicates whether the current-depth encoding unit is divided into lower-depth encoding units.

The prediction unit 910 for the prediction encoding of the coding units of depth 0 and 2N_0x2N_0 has a partition type 912 of 2N_0x2N_0 size, a partition type 914 of 2N_0xN_0 size, a partition type 916 of N_0x2N_0 size, a partition of size N_0xN_0 Type < / RTI >

For each partition type, predictive encoding should be repeatedly performed for each prediction unit of 2N_0x2N_0 size, two 2N_0xN_0 size prediction units, two N_0x2N_0 size prediction units, and four N_0xN_0 size prediction units. For a prediction unit of size 2N_0x2N_0, size N_0x2N_0, size 2N_0xN_0, and size N_0xN_0, motion prediction can be performed in intra mode and inter mode. The skip mode can be performed only for the prediction unit of size 2N_0x2N_0.

If the coding error by the partition type 918 of the size N_0xN_0 is the smallest, the depth 0 is changed to 1 (920), and the coding units 922, 924, 926 and 928 of the partition type of the depth 2 and the size N_0xN_0 are changed The minimum coding error can be repeatedly searched for.

Since encoding is repeatedly performed on the encoding units 922, 924, 926, and 928 of the same depth, encoding of only one of the encoding units of depth 1, for example, will be described. The prediction unit 930 for predicting the coding unit of the depth 1 and the size 2N_1x2N_1 (= N_0xN_0) includes a partition type 932 of size 2N_1x2N_1, a partition type 934 of size 2N_1xN_1, a partition type 936 of size N_1x2N_1, , And a partition type 938 of size N_1xN_1. For each partition type, predictive coding should be repeatedly performed for each prediction unit of a size 2N_1x2N_1, a prediction unit of two sizes 2N_1xN_1, a prediction unit of two sizes N_1x2N_1, and a prediction unit of four sizes N_1xN_1.

If the coding error by the partition type 938 of the size N_1xN_1 is the smallest, the coding units 942, 944, 946 and 948 of the depth 2 and the size N_2xN_2 are changed while changing the depth 1 to the depth 2 (940) The minimum coding error can be repeatedly searched for.

If the maximum depth is d, the depth-based segmentation information can be set until the depth d-1. That is, the prediction unit 950 for predictive coding of the coding unit of the depth d-1 and the size 2N_ (d-1) x2N_ (d-1) A partition type 954 of size 2N_ (d-1) xN_ (d-1), a partition type 956 of size N_ (d-1) x2N_ 1) xN_ (d-1) < / RTI >

(D-1) x2N_ (d-1), two predicted units of two sizes 2N_ (d-1) ) prediction unit of x2N_ (d-1), x2N_ (d-1), and four sizes N_ (d-1) xN_ (d-1). Since the maximum depth is d, the coding unit 952 of depth d-1 no longer undergoes the division process.

The image encoding apparatus 100 according to an exemplary embodiment of the present invention compares depth-based encoding errors to determine depths for encoding units 912 and selects the depths at which the smallest encoding error occurs. For example, a coding error for a coding unit of depth 0 is predicted for each partition type 912, 914, 916, and 918, and a prediction unit in which the smallest coding error occurs is determined. Similarly, a prediction unit having the smallest coding error can be searched for every depth 0, 1, ..., d-1. At the depth d, the coding error can be determined through predictive coding based on the prediction unit 960, which is a coding unit of size 2N_dx2N_d. In this way, the minimum coding errors of the depths 0, 1, ..., d-1, and d are compared with each other, and the depth with the smallest error is selected to be determined as the coding depth. The coding depth and the prediction unit of the corresponding depth can be encoded and transmitted as information on the coding mode. In addition, since the coding unit must be divided from the depth 0 to the coding depth, only the division information of the coding depth is set to '0', and the division information by depth is set to '1' except for the coding depth.

The encoding information extracting unit 220 of the image decoding apparatus 200 according to an embodiment of the present invention extracts information on the encoding depth and the prediction unit for the encoding unit 912 and uses the information on the encoding depth 912 to decode the encoding unit 912 . The image decoding apparatus 200 according to an exemplary embodiment of the present invention uses the division information according to the depth to determine the depth with the division information of '0' as a coding depth and can use it for decoding using the information about the coding mode for the corresponding depth have.

FIGS. 10A, 10B, and 10C illustrate the relationship between an encoding unit, a prediction unit, and a frequency conversion unit according to an embodiment of the present invention.

The encoding unit 1010 is encoding units for encoding depth determined by the image encoding apparatus 100 according to the embodiment with respect to the maximum encoding unit. The prediction unit 1060 is a prediction unit of each coding depth unit among the coding units 1010 and the conversion unit 1070 is a conversion unit of each coding depth unit.

When the depth of the maximum encoding unit is 0, the depth of the encoding units 1012 and 1054 is 1 and the depth of the encoding units 1014, 1016, 1018, 1028, 1050, The coding units 1020, 1022, 1024, 1026, 1030, 1032 and 1048 have a depth of 3 and the coding units 1040, 1042, 1044 and 1046 have a depth of 4.

A portion (1014, 1016, 1022, 1032, 1048, 1050, 1052, 1054) of the prediction units 1060 is a type in which the coding unit is divided. That is, the prediction units 1014, 1022, 1050 and 1054 are partition types of 2NxN, the prediction units 1016, 1048 and 1052 are partition types of Nx2N, and the prediction units 1032 are partition types of NxN. That is, the prediction unit of the depth-dependent coding units 1010 is smaller than or equal to each coding unit.

The image data of a part 1052 of the conversion units 1070 is subjected to frequency conversion or frequency inverse conversion in units of data smaller in size than the encoding unit. The conversion units 1014, 1016, 1022, 1032, 1048, 1050, 1052, and 1054 are data units of different sizes or types when compared with the prediction units of the prediction units 1060. That is, the image encoding apparatus 100 and the image decoding apparatus 200 according to an exemplary embodiment of the present invention perform prediction and frequency conversion / inverse transform operations on the same encoding unit, respectively, based on separate data units .

FIG. 11 shows encoding information for each encoding unit according to an embodiment of the present invention.

The output unit 130 of the image encoding apparatus 100 according to an exemplary embodiment of the present invention outputs encoding information for each encoding unit and outputs the encoding information to the encoding information extracting unit 200 of the image decoding apparatus 200 according to an embodiment of the present invention 220) can extract the encoding information for each encoding unit.

The encoding information may include division information for the encoding unit, partition type information, prediction mode information, and conversion unit size information. The encoding information shown in FIG. 11 is only an example that can be set in the image encoding apparatus 100 and the image decoding apparatus 200 according to an embodiment of the present invention, and is not limited to the illustrated ones.

The division information may indicate the coding depth of the corresponding encoding unit. That is, since depths that are no longer divided according to the division information are coding depths, partition type information, prediction mode, and conversion unit size information can be defined with respect to the coding depth. If it is necessary to further divide by one division according to the division information, encoding should be performed independently for each of the four higher-depth-depth coding units.

As the partition type information, the partition type of the conversion unit of the coding unit of the coding depth can be represented by 2Nx2N, 2NxN, Nx2N and NxN. The prediction mode may indicate the motion prediction mode as one of an intra mode, an inter mode, and a skip mode. The intra mode and the inter mode can be defined in the partition types 2Nx2N, 2NxN, Nx2N and NxN, and the skip mode can be defined only in the partition type 2Nx2N. The conversion unit size can be set to two kinds of sizes in the intra mode and two kinds of sizes in the inter mode.

The encoding unit-specific encoding information of the belonging encoding depth may be stored for each minimum encoding unit in the encoding unit. Therefore, if encoding information held in each of the adjacent minimum encoding units is checked, it can be confirmed whether or not the encoding information is included in the encoding unit of the same encoding depth. In addition, since the encoding unit of the encoding depth can be identified by using the encoding information held in the minimum encoding unit, the distribution of encoding depths in the maximum encoding unit can be inferred.

In this case, when the current encoding unit is predicted with reference to the neighboring data unit, the encoding information of the minimum encoding unit in the depth encoding unit adjacent to the current encoding unit is directly used, so that the data of the minimum encoding unit can be referred to.

In yet another embodiment, the encoding information of the depth encoding unit may be stored only for the minimum encoding unit represented in the depth encoding unit. In this case, when the current encoding unit is predicted by referring to the surrounding encoding unit, the data adjacent to the current encoding unit in the depth encoding unit may be retrieved using the encoding information of the adjacent depth encoding unit.

The intraprediction performed by the intraprediction unit 410 of the video encoding apparatus 100 and the intraprediction unit 550 of the video decoding apparatus 200 according to an embodiment of the present invention shown in FIG. This will be described in detail. In the following description, a coding unit is a term referring to a block currently coded in an image coding step, and a decoding unit is a term referring to a block to be currently decoded in an image decoding step. The terms encoding unit and decode unit are merely the difference between the encoding step and the decoding step of the image and the encoding unit in the encoding step may be referred to as a decode unit in the decode step. For the sake of uniformity of terms, except for special cases, they shall be uniformly coded in the coding step and the decoding step in the same coding unit. In addition, it should be understood that the intra prediction method and apparatus according to an exemplary embodiment of the present invention can be applied to intra prediction in a general image codec, as well as those of ordinary skill in the art to which the present invention belongs .

FIG. 12 shows the number of intra prediction modes according to the size of an encoding unit according to an embodiment of the present invention.

According to an embodiment of the present invention, the number of intra prediction modes to be applied to a coding unit can be variously set according to the size of a coding unit (decoding unit in the decoding step). For example, referring to FIG. 12, the number of intraprediction modes actually performed for each of the 2x2, 4x4, 8x8, 16x16, 32x32, 64x64, and 128x128 encoding units is NxN, 5, 9, 9, 17, 33, 5, and 5 (in the case of Example 2). The reason for differentiating the number of actually performed intraprediction modes according to the size of the encoding unit is that the overhead for encoding the prediction mode information differs depending on the size of the encoding unit. In other words, in the case of a small-sized coding unit, the overhead for transmitting the additional information such as the prediction mode of the small coding unit may increase although the portion occupying the entire image is small. Therefore, when a small coding unit is coded in too many prediction modes, the bit amount increases and the compression efficiency may be lowered. In addition, since a coding unit having a large size, for example, a coding unit having a size of 64x64 or more is generally selected as a coding unit for a flat region of an image, a coding unit having a large size Encoding of an encoding unit into too many prediction modes may also be inefficient in terms of compression efficiency.

Therefore, according to an embodiment of the present invention, the coding unit is composed of N1xN1 (2≤N1≤8, N1 is an integer), N2xN2 (16≤N2≤32, N2 is an integer), N3xN3 (A1 is a positive integer), and the number of intra prediction modes to be performed for each coding unit having a size of N2xN2 is defined as the number of intra prediction modes to be performed for each coding unit having the size N1xN1 A2 (A2 is a positive integer), and the number of intra prediction modes to be performed for each coding unit having a size of N3xN3 is A3 (A3 is a positive integer), the size of each coding unit It is desirable to set the number of intra prediction modes to be performed according to the number of intra prediction modes. That is, when the current picture is categorized into a small-sized coding unit, a medium-sized coding unit, and a large-sized coding unit, the medium-sized coding unit has the largest number of prediction modes, And a coding unit of a large size are set to have a relatively smaller number of prediction modes. However, the present invention is not limited to this, and it may be possible to set a larger number of prediction modes for small and large size coding units. The number of prediction modes according to the size of each coding unit shown in FIG. 12 is only one embodiment, and the number of prediction modes according to the size of each coding unit can be changed.

13A is a diagram for explaining an example of an intra prediction mode applied to a coding unit of a predetermined size according to an embodiment of the present invention.

Referring to FIGS. 12 and 13A, for example, a vertical mode (mode 0), a horizontal mode (mode 1), a DC (direct current) mode (Mode 2), Diagonal Down-Left Mode (Mode 3), Diagonal Down-Right Mode (Mode 4), Vertical-Right Mode (Mode 5) (Mode 6), Vertical-Left (Mode 7), and Horizontal-Up (Mode 8) modes.

13B is a diagram showing the directions of the intra prediction modes of FIG. 13A. The number at the end of the arrow in FIG. 13B indicates the corresponding mode value when the prediction is performed in that direction. Mode 2 is not shown as a directional DC prediction mode.

13C is a diagram illustrating an intra prediction method for the encoding unit shown in FIG. 13A.

Referring to FIG. 13C, a prediction encoding unit is generated using A - M, which is a peripheral pixel of the current encoding unit, according to the available intra prediction mode determined by the size of an encoding unit. For example, an operation of predicting a 4 × 4 current encoding unit according to the mode 0, ie, the vertical mode in FIG. 13A, will be described. First, the pixel values of the pixels A to D adjacent to the upper side of the current encoding unit of 4 × 4 size are predicted as pixel values of the 4 × 4 current encoding unit. That is, the value of the pixel A is divided into four pixel values included in the first column of the 4x4 current coding unit, the pixel B is divided into four pixel values included in the second column of the 4x4 current coding unit, Is predicted to the four pixel values included in the third column of the 4x4 current encoding unit and the pixel D value is predicted to the four pixel values included in the fourth column of the 4x4 current encoding unit. Next, an error value is calculated by subtracting the 4x4 current encoding unit predicted using the pixels A to D and the actual value of the pixel included in the original 4x4 current encoding unit, and the error value is encoded.

14 is a view for explaining another example of an intra prediction mode applied to a coding unit of a predetermined size according to an embodiment of the present invention.

Referring to FIGS. 12 and 14, for example, in the intra prediction of a 2 × 2 encoding unit, a vertical mode, a horizontal mode, a DC (Direct Current) mode, a plane mode, And a right (Diagonal Down-Right) mode.

On the other hand, as shown in FIG. 12, when an encoding unit having a size of 32x32 has 33 intra-prediction modes, it is necessary to set the directions of 33 intra-prediction modes. In an embodiment of the present invention, in addition to the intraprediction modes as shown in FIGS. 13 and 14, in order to set intra prediction modes in various directions, a method for selecting a neighboring pixel to be used as a reference pixel, The prediction direction is set using the dx and dy parameters. For example, when 33 prediction modes are defined as mode N (N is an integer from 0 to 32), mode 0 is a vertical mode, mode 1 is a horizontal mode, mode 2 is a DC mode, and mode 3 is a plane mode (1, 1), (1,1), (1,2), (2,1), (1, -2), (2) (1, -2), (2, -1), (2, -11), (5, -7) , (1,11), (1,1), (12,3), (1,11), (1,7), (3,10), 7, -6), (7, -4), (11,1), (6,1), (8,3), (5,3), (5,7) 5, -7), (4, 3) by using a (dx, dy) is expressed with a value of can be defined as a prediction mode having a directionality of tan ^-1 (dy / dx).

mode # dx dy mode # dx dy mode 4 One -One mode 18 One -11 mode 5 One One mode 19 One -7 mode 6 One 2 mode 20 3 -10 mode 7 2 One mode 21 5 -6 mode 8 One -2 mode 22 7 -6 mode 9 2 -One mode 23 7 -4 mode 10 2 -11 mode 24 11 One mode 11 5 -7 mode 25 6 One mode 12 10 -7 mode 26 8 3 mode 13 11 3 mode 27 5 3 mode 14 4 3 mode 28 5 7 mode 15 One 11 mode 29 2 7 mode 16 One -One mode 30 5 -7 mode 17 12 -3 mode 31 4 -3 mode 0 is a vertical mode, mode 1 is a horizontal mode, mode 2 is a DC mode, mode 3 is a plane mode, and mode 32 is a bi-linear mode.

The last mode 32 may be set to a bilinear mode using bilinear interpolation as described below using FIG.

15 is a reference diagram for explaining intra prediction modes having various directions according to an embodiment of the present invention.

As described above with reference to Table 1, the intra-prediction modes according to an exemplary embodiment of the present invention may have various directions of tan ^-1 (dy / dx) using a plurality of (dx, dy)

Referring to FIG. 15, the angle of tan ^-1 (dy / dx) determined according to the value of each mode (dx, dy) shown in Table 1 around the current pixel P to be predicted in the current encoding unit The neighboring pixels A and B located on the extension line 150 having the current pixel P can be used as a predictor of the current pixel P. [ In this case, the neighboring pixels used as the predictor are preferably pixels of the previous coding unit on the upper side and the left side of the current coding unit, which have been previously encoded and restored. Further, a peripheral pixel closer to the extension line 150 can be used as a predictor of the current pixel P when the extension line 150 passes between pixels around the integer position rather than around the integer position. As shown in the figure, when there are two neighboring pixels of the upper side neighboring pixel A and the left neighboring pixel B that meet the extension line 150, the upper neighboring pixel A and the left neighboring pixel B Is used as the predictor of the current pixel P or when the dx * dy value is positive, the upper neighboring pixel A is used and when the dx * dy value is negative, the neighboring pixel B is used. Can be used.

It is preferable that the intraprediction modes having various directions as shown in Table 1 are set in the encoding and decoding stages in advance so that only the corresponding indexes of the intra prediction modes set for each encoding unit are transmitted.

16 is a reference diagram for explaining a bilinear mode according to an embodiment of the present invention.

Referring to FIG. 16, a bi-linear mode is a mode in which a current pixel P and its neighboring pixel values around the current pixel P to be predicted in the current encoding unit, And the resultant value is used as a predictor of the current pixel P, as shown in FIG. That is, in the bilinear mode, the pixel A 161, the pixel B 162, the pixel D 166, and the pixel E 167 located at the upper, lower, left and right boundaries of the current pixel P as a predictor of the current pixel P A geometric average value of the distances to the upper, lower, left, and right boundaries of the current pixel P is used. In this case, since the bilinear mode is also one of the intra prediction modes, it is necessary to use the reconstructed upper and left surrounding pixels as reference pixels at the time of prediction. Therefore, instead of using the corresponding pixel value in the current encoding unit as the pixel A 161 and the pixel B, the virtual pixel value generated using the upper and left peripheral pixels is used.

Specifically, by calculating the average value of the upper leftmost neighboring pixel (RightUpPixel) 164 and the lower leftmost neighboring pixel (LeftDown Pixel) 165 adjacent to the current encoding unit as shown in the following Equation 1, Lt; RTI ID = 0.0 > C (163) < / RTI >

The virtual pixel A 161 located at the lowermost boundary when the current pixel P is extended to the lower end in consideration of the distance W 1 to the left border of the current pixel P and the distance W 2 to the right border ) Is calculated as shown in the following equation (2).

Similarly, when the current pixel P is extended to the right in consideration of the distance h1 to the upper boundary of the current pixel P and the distance h2 to the lower boundary, the imaginary pixel B ( 162) is calculated according to the following equation (3).

When the values of the virtual pixel A 161 on the lower boundary line of the current pixel P 160 and the imaginary pixel B 162 on the right boundary line are determined using Equations 1 to 3, the average value of A + B + D + E May be used as a predictor of the current pixel P (160). Such a bilinear prediction process is applied to all the pixels in the current encoding unit, and a predictive encoding unit of the current encoding unit according to the bilinear prediction mode is generated.

According to an embodiment of the present invention, predictive coding is performed according to various intra prediction modes set according to the size of a coding unit, thereby enabling more efficient compression according to the characteristics of an image.

According to an embodiment of the present invention, since a large number of intra prediction modes are used in comparison with the number of intra prediction modes used in the conventional codec according to the size of an encoding unit, compatibility with the conventional codec may be a problem. According to the prior art, up to nine intra prediction modes are available as shown in Figures 13A and 13B. Therefore, it is necessary to map the intra-prediction modes of various directions selected according to an embodiment of the present invention to one of a smaller number of intra-prediction modes. That is, when the number of intra prediction modes available for the current coding unit is N1 (N1 is an integer), a prediction mode having a predetermined size having N2 (N2 is an integer) intraprediction modes different from the available intra prediction modes of the current coding unit The intra prediction mode of the current coding unit may be mapped to the intra prediction mode of the most similar intra prediction mode among the N2 intra prediction modes for the compatibility of the coding units. For example, a total of 33 intra prediction modes are available for the current coding unit as shown in Table 1, and the intra prediction mode finally applied to the current coding unit is mode 14, i.e. (dx, dy) = (4, 3), it is assumed that tan ^-1 (3/4) is approximately 36.87 (degrees). In this case, in order to match the intra prediction mode applied to the current block to one of nine intra prediction modes as shown in FIGS. 13A and 13B, a mode 4 (down_right) mode having the direction most similar to 36.87 . That is, the mode 14 in Table 1 can be mapped to the mode 4 shown in FIG. 13A. Similarly, when the intra prediction mode applied to the current encoding unit is selected as a mode 15, i.e., (dx, dy) = (1,11) among a total of 33 available intra prediction modes in Table 1, Since the directionality of the intra-prediction mode has tan ^-1 (11)? 84.80 (degrees), it can be mapped to the mode 0 (vertical) mode of FIG. 13B most similar to this directionality.

On the other hand, in order to decode an encoding unit encoded through intraprediction, prediction mode information on which intra-prediction mode the current encoding unit is encoded is required. Therefore, when encoding the image, information about the intra-prediction mode of the current encoding unit is added to the bitstream. When the intra-prediction mode information is directly added to the bitstream for each encoding unit, overhead is increased and the compression efficiency is lowered have.

Therefore, in an embodiment of the present invention, instead of directly transmitting the information on the intra prediction mode of the current coding unit determined as a result of coding of the current coding unit, the predicted value of the intra prediction mode predicted from the surrounding coding unit and the intra prediction mode Only the difference value is transmitted.

17 is a diagram for explaining a process of generating a prediction value of an intra prediction mode of a current encoding unit according to an embodiment of the present invention.

Referring to FIG. 17, when the current coding unit is A (170), the intra prediction mode of the current coding unit A 170 can be predicted from the intra prediction mode determined in the surrounding coding units. For example, if the determined intra prediction mode of the left coding unit B 171 of the current coding unit A 170 is mode 3 and the intra prediction mode of the upper coding unit C 172 is mode 4, The intra prediction mode of the coding unit 170 may be predicted as a mode 3 having a smaller one of the prediction modes of the upper coding unit C 172 and the left coding unit B 171. If the intraprediction mode determined as a result of the actual intraprediction encoding for the current encoding unit A 170 is mode 4, only intra-prediction mode information 1, which is a difference between the intra-prediction mode value predicted from the surrounding encoding units, Prediction mode of the current decoding unit in the same manner as described above and adds the mode difference value transmitted through the bitstream to the prediction value of the intra prediction mode to generate an intra prediction mode actually applied to the current decoding unit, Information can be obtained. In the above description, only the surrounding encoding units located on the upper and left sides of the current encoding unit are used. However, intra-prediction of the current encoding unit A 170 using other surrounding encoding units such as E and D in FIG. The mode can be predicted.

Since the intraprediction modes actually performed are different according to the sizes of the coding units, the intra prediction mode predicted from the surrounding coding units may not match the intra prediction mode of the current coding unit. Therefore, in order to predict the intra prediction mode of the current encoding unit from neighboring encoding units having different sizes, a mapping process for unifying the intra prediction modes among the encoding units having different intra prediction modes is required.

18 is a reference diagram for explaining a process of mapping an intra prediction mode between coding units having different sizes according to an embodiment of the present invention.

Referring to FIG. 18, it is assumed that the current coding unit A 180 has a size of 16 × 16, the left coding unit B 181 has an 8 × 8 size, and the upper coding unit C 182 has a size of 4 × 4. Also, as in the first example of FIG. 12, it is assumed that the number of intra prediction modes available in 4x4, 8x8, and 16x16 coding units is 9, 9, and 33, respectively. In this case, since the intra prediction modes available in the left encoding unit B 181 and the upper encoding unit C 182 are different from the intra prediction modes available in the current encoding unit A 180, the left encoding units B 181 and The intra prediction mode predicted from the upper side encoding units C 182 is not suitable for use as the predicted value of the intra prediction mode of the current encoding unit A 180. Therefore, according to an embodiment of the present invention, the intra prediction mode of the surrounding encoding units B and C (181, 182) is divided into first and second representative intra prediction modes in the most similar direction among the predetermined number of representative intra prediction modes And selects the final representative intra prediction mode having the smaller one of the first and second representative intra prediction modes. The intra prediction mode having the direction most similar to the selected representative intra prediction mode among the available intra prediction modes according to the size of the current coding unit A 180 is predicted as the intra prediction mode of the current coding unit.

19 is a reference diagram for explaining a process of mapping intra-prediction modes of a surrounding encoding unit to one of representative intra-prediction modes according to an embodiment of the present invention. FIG. 19 shows a case in which vertical, horizontal, DC, diagonal left, diagonal right, vertical right, vertical left, horizontal right, and horizontal right modes are set as representative intra prediction modes have. However, the representative intra-prediction mode is not limited to the illustrated one, and may be set to have various numbers of directions.

Referring to FIG. 19, a predetermined number of representative intra prediction modes are set in advance, and the intra prediction mode of the surrounding encoding unit is mapped to the representative intra prediction mode of the most similar direction. For example, if the determined intra prediction mode of the upper coding unit A has a direction indicated by the MODE_A 190, the intra prediction mode MODE_A 190 of the upper coding unit A includes nine preset representative intra prediction Is mapped to MODE 1 having the most similar direction among the modes 1 to 9. Likewise, if the determined intra prediction mode of the left encoding unit B has the direction shown by MODE_B 191, then the intra prediction mode MODE_B 191 of the left encoding unit B has 9 preset representative intra prediction modes 1 To 9, which has the most similar direction among the nine directions.

An intra prediction mode having a smaller mode value from among the first representative intra prediction mode and the second representative intra prediction mode is selected as the representative intra prediction mode of the final peripheral encoding unit. The reason why the representative intra prediction mode having such a smaller mode value is selected is because a smaller mode value is set for the more frequently occurring intra prediction modes. That is, when a different intra-prediction mode is predicted from neighboring encoding units, the intra-prediction mode having a smaller mode value is a prediction mode having a higher probability of occurrence. Therefore, when different prediction modes are contended, It is preferable to select a prediction mode having a smaller mode value as a predictor of the prediction mode.

Even when the representative intra prediction mode is selected from the surrounding encoding unit, the representative intra prediction mode may not be used as the predictor of the intra prediction mode of the current encoding unit. If the current coding unit A 180 has 33 intra prediction modes and the representative intra prediction mode has only 9 intra prediction modes as shown in FIG. 18, the current coding unit A 180 corresponding to the representative intra prediction mode ) Does not exist in the intra prediction mode. In such a case, similar to mapping the intra-prediction mode of the above-described surrounding encoding unit to the representative intra-prediction mode, intra-prediction having a direction most similar to the selected representative intra-prediction mode among the intra- Mode can be finally selected as the intra prediction mode predictor of the current encoding unit. For example, if the representative intra prediction mode finally selected from the surrounding coding unit is mode 1 in FIG. 19, an intra prediction mode having the direction most similar to the mode 1 among the available intra prediction modes according to the size of the current coding unit is And is finally selected as a predictor of the intra prediction mode of the current encoding unit.

20 is a block diagram illustrating an apparatus for intra prediction of an image according to an embodiment of the present invention. The intra prediction apparatus 2000 according to an embodiment of the present invention includes an intra prediction unit 410 of the image coding apparatus 400 and an intra prediction unit 550 of the image decoding apparatus 500 of FIG. As shown in FIG.

Referring to FIG. 20, the intra-prediction mode determining unit 2010 determines an intra-prediction mode to be applied to the current encoding unit according to the sizes of the respective encoding units based on the maximum encoding unit and the depth, as described above. That is, the intra-prediction mode determining unit 2010 selects intra-prediction mode candidates to be applied according to the size of the current encoding unit among intra-prediction modes in various directions.

The intra-prediction mode execution unit 2020 performs intra-prediction on each coding unit by applying the determined intra-prediction modes. The optimal intra prediction mode having the minimum error value is determined as the final intra prediction mode of the coding unit based on the error value between the predicted coding unit generated by the intra prediction mode performing unit 2020 and the original coding unit.

When the intraprediction apparatus 2000 shown in FIG. 20 is used in a decoding apparatus, the intra prediction mode determination unit 2010 determines the maximum encoding Unit, the depth information which is the hierarchical division information of the maximum encoding unit, determines the size of the current decoding unit, and determines the intra prediction mode to be performed using the intra prediction mode information applied to the current decoding unit. In addition, the intra-prediction mode performing unit 2020 performs intra-prediction on the decoding unit according to the extracted intra-prediction mode to generate a predictive decoding unit. The predictive decoding unit is added to the residual data reconstructed from the bitstream to decode the decoding unit.

FIG. 21 is a flowchart illustrating an image encoding method according to an embodiment of the present invention.

Referring to FIG. 21, in step 2110, the current picture is divided into at least one block. As described above, the current picture can be divided based on the maximum encoding unit, which is the encoding unit having the maximum size, and the depth, which is the hierarchical division information of the maximum encoding unit.

In step 2120, an intra prediction mode to be performed for the current block is determined according to the size of the divided current block. As described above, according to one embodiment of the present invention, the intra-prediction mode is a mode in which a block located on an extension line having an angle of tan ^-1 (dy / dx) around each pixel in the current block, And a prediction mode for performing prediction using a pixel.

In step 2130, intra prediction for the current block is performed according to the determined intra prediction mode. The intra prediction mode having the smallest prediction error value among the intra prediction modes is selected as the final intra prediction mode of the current block.

22 is a flowchart illustrating a video decoding method according to an embodiment of the present invention.

Referring to FIG. 22, in step 2210, the current picture is divided into at least one block of a predetermined size. Here, the current picture may be divided based on the maximum decoding unit which is the decoding unit having the maximum size extracted from the bit stream and the depth information which is the hierarchical division information of the maximum decoding unit.

In step 2220, the intra prediction mode information applied to the current block is extracted from the bitstream. The intraprediction mode is a mode in which prediction is performed using pixels of a neighboring block located on an extension line having an angle of tan ^-1 (dy / dx) (dx, dy is an integer) centered on each pixel of the current block, And a prediction mode for performing a prediction mode. As described above with reference to Figs. 17 to 19, when the intra prediction mode predictor predicted from the intra prediction modes of the peripheral decoding unit is used, the intra prediction modes of the neighbor decoding units of the current decoding unit are referred to as representative intra prediction modes And then selects a representative intra-prediction mode having a smaller mode value among the representative intra-prediction modes as a final representative intra-prediction mode. The intra prediction mode having the direction most similar to the last representative intra prediction mode among the available intra prediction modes determined according to the size of the current decoding unit is selected as the predictor of the intra prediction mode of the current decoding unit, The intraprediction mode of the current decoding unit can be determined by extracting a difference value between predictors of the actual intra prediction mode and the intra prediction mode and adding the difference value to the predictor of the intra prediction mode.

The intra prediction for the decoding unit is performed according to the intra prediction mode extracted in step 2230 to decode the decoding unit.

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium. The computer readable recording medium may be a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (2)

Extracting intra prediction mode information applied to a current block to be decoded from the bitstream; And
And performing intra prediction on the current block according to the extracted intra prediction mode information,
The intra-prediction mode
Wherein the specific direction is indicated by one of horizontal direction dx (dx is an integer) and vertical direction dy (dy is an integer)
The step of performing the intra prediction
Obtaining at least one neighboring pixel located at one of left and upper sides of the current block in accordance with the position of the current pixel of the current block and the specific direction indicated by the intra prediction mode;
Obtaining a predicted value of a current pixel based on one surrounding pixel when the number of the at least one neighboring pixel is one; And
Obtaining a predicted value of the current pixel based on a weighted average value of two neighboring pixels when the number of the at least one neighboring pixels is two,
Wherein the image is divided into a plurality of maximum encoding units according to information on a size of a maximum encoding unit,
Wherein the maximum coding unit is hierarchically divided into a plurality of coding units having depths according to the division information,
The encoding unit of the current depth is one of the square data units divided from the encoding unit of the higher depth,
Wherein if the division information indicates division at the current depth, the current-depth encoding unit is divided into sub-depth encoding units independently of the surrounding encoding units,
Wherein at least one prediction unit is obtained from the coding unit of the lower depth when the division information indicates that the division information is not divided at the lower depth. An entropy decoding unit for extracting intra prediction mode information applied to a current block decoded from a bitstream; And
And an intra prediction unit for performing intra prediction on the current block according to the extracted intra prediction mode information,
The intra-prediction mode
Wherein the specific direction is indicated by one of horizontal direction dx (dx is an integer) and vertical direction dy (dy is an integer)
The intra-
Obtaining at least one neighboring pixel located at one of left and upper sides of the current block according to the position of the current pixel of the current block and the specific direction indicated by the intra prediction mode,
Acquiring a predicted value of a current pixel based on one surrounding pixel when the number of the at least one neighboring pixels is one,
Obtaining a predicted value of the current pixel based on a weighted average value of two neighboring pixels when the number of the at least one neighboring pixels is two,
Wherein the image is divided into a plurality of maximum encoding units according to information on a size of a maximum encoding unit,
Wherein the maximum coding unit is hierarchically divided into a plurality of coding units having depths according to the division information,
The encoding unit of the current depth is one of the square data units divided from the encoding unit of the higher depth,
Wherein if the division information indicates division at the current depth, the current-depth encoding unit is divided into sub-depth encoding units independently of the surrounding encoding units,
Wherein at least one prediction unit is obtained from the lower-depth coding unit when the division information indicates that the lower-depth information is not divided.

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